Pathogen: caused by parasitic worms or flukes Schistosoma mansoni, S. haematobium, and S. japonicum
Category of Pathogen: Phylum: Platyhelminthes or the flat worms of the Class: Trematoda commonly known as flukes.
Name of the Disease Caused by the Pathogen: Schistosomiasis or bilharzia (bill-HAR-zi-a), can also be called snail fever or the hydroelectric disease, because of its impact in areas with dams.
Symptoms of the Infection: After a few days of the initial contact, the skin begins to become itchy and a rash may form. Coughing, chills, fever and muscle aches can occur after 1-2 of the initial contact, but most people do not have any symptoms at this early of phase.
In the chronic form of the disease, generally, the worms themselves do not cause the symptoms of this disease but from the eggs they produce and the immune response our body uses to attack the antigens. The eggs travel to the bladder, intestine or the liver causing scarring and inflammation. This can lead to damage of the liver, bladder and lungs, but in a very few cases the eggs can travel to the brain causing spinal cord inflammation and seizures . Children that are infected more than once can develop learning disabilities, anemia, malnutrition, and inhibit growth.
In the acute form of the disease called Katayama’s fever symptoms can be more varied, some of these include: Abdominal pain, cough, diarrhea, fatigue, eosinphilia-extemely high white blood count, fever, inflammation of the liver and spleen, genital sores-can lead to secondary infection and higher susceptibility of HIV that can be alleviated with early treatment, brain lesions and dermatitis of the feet.
Primary Host: Snails, specifically freshwater snails.
Other Hosts: Humans
Route of Transmission: The eggs of the worm are excreted in feces or urine of a human and the moment they touch the water they “hatch and the parasite called the miracidium needs to find a freshwater snail host to survive. Once inside the snail, the parasite divides into thousands of new parasites called cercariae. This stage in the life cycle of the worm does not harm the snail. These are then excreted through the snail’s foot into the water where it begins to search for its secondary host, humans. The parasite can survive up to 48 hours without a secondary host. The cercariae can penetrate a human’s skin in seconds, thus beginning the cycle anew. It will take around 4 to 6 weeks for the worm to mature into either a male or female. The female can lay 200 to 2000 eggs per day for up to five years. In most cases only half the eggs are released form the body, the others remain in the vital organs creating many symptoms, some even leading to cancer or organ failure.
Ro=1 The disease will remain at a steady level in the host population.
Prevalence: This parasite is endemic to 74 tropical countries and is thought be found in over 200 million people right now, with 600 million people at risk.
Prevalence
Generation Time: The generation time is around 6 to 8 weeks for the parasite to go from egg to mature worm that reproduces.
Mortality Rate: According to a study that was done in Sudan in 1999, the estimated mortality rate is 1/1000 infected. The disease has a relatively low mortality rate but a significantly high morbidity rate.
Morbidity Rate: The morbidity rate is very high because this disease can be a chronic illness that can be debilitating for the millions that suffer from it. Some of the side effects can be cancer or vital organ inflammation/failure.
Is it preventable?: Yes, this disease is completely preventable. Education, Diagnosis and Treatment, Adequate health care facilities and clean drinking water, management of the environment-through control of the primary host-freshwater snails are the most important ways for the eradication of this disease that infects 200 million people worldwide. The most important part of the prevention of this disease is the installing and monitoring of a clean water supply. Not only for drinking water, but for hygienic uses also. The second fundamental aspect of the prevention of this disease is education, the individuals in high risk areas need to be aware of the basic ways they can prevent infection and the spread of this disease, mainly though hygienic practices. Diagnosis and treatment go hand and hand with education, the people at risk should know the symptoms and the vectors for this disease.
The disease is treated using a single dose of Praziquantrel, which is a drug used to rid the body of flatworms. There is also a vaccine that is in the preliminary stages that would stop the end stages of the worms life cycle in humans.
Does this disease trigger long lasting immunity?: No, this is a parasite that can reinfect the secondary host at any time in the host’s life.
When was the pathogen first described?: This disease goes back all the way to the Pharaohs in Egypt, but the parasite was first described by a German pathologist named Theodr Bilhraz in 1851. The entire disease cycle was first described by Brazilian parasitologist Manuel Augusto Piraja da Silva in 1908.
What is the economic impact of this disease: This disease is a devastating socioeconomic disease second only to malaria. This disease mainly affects adults who are employed in the fishing and agricultural areas, but it is estimated that 66 million children have the disease, which effects their cognitive and
The coolest thing about the disease: An interesting fact about this disease occurs because of the increased damming and irrigation of the Nile, the proliferation of this disease in the surrounding areas was devastating. As a counter attack from the 1950s to the early 1980s people were treated with many shots of tartar ememic (a derivative of tartic acid found in red wine for instance). There is an idea that this inadvertently caused the Hepatitis C epidemic that has occurred in Egypt through the use of dirty needles. Egypt has the highest incidence of Hepatitis C of anywhere in the world and this seems to directly coincide with the occurrence of schistosomiasis.
Citations for the information included:
“International Travel and Health.” World Health Organization. 1 Sep. 2009 <gamapserver.who.int/mapLibrary/Files/Maps/Global_ShistoPrevalence_I
Kheir, Musa M., Isam A. Eltoum, Ahmed M. Saad, et al. “Mortality Due To Schistosomiasis Mansoni: A Field Study In Sudan.” The American Journal of Tropical Medicine and Hygiene. 31 Aug. 2009 <www.ajtmh.org/cgi/reprint/60/2/307.pdf>.
“Professor Andre Capron.” Lebanese Academy of Science. 31 Aug. 2009 <www.asliban.org/images/Schistosomiasis.jpg>.
“Schistosomiasis – Wikipedia, the free encyclopedia.” Wikipedia, the free encyclopedia. 9 Aug. 1929. 1 Sep. 2009 <http://en.wikipedia.org/wiki/Schistosomiasis>.
“Schistosomiasis.” Center for Disease Control. 26 Feb. 2008. 31 Aug. 2009 <www.cdc.gov/ncidod/dpd/parasites/schistosomiasis/factsht_schistosomiasis.htmf>.
“Schistosomiasis.” MicrobiologyBytes. 28 Jan. 2007. 1 Sep. 2009 <http://www.microbiologybytes.com/introduction/Schisto.html>.
